From the viewpoint of the conservation of natural environment, researches on aliphatic polyesters biodegradable in natural environment have been eagerly undertaken. Among them, polylactic acid is expected as molding materials, for example for packaging materials such as container, film or the like, fabric materials such as clothing, floor mat, interior material for automobile or the like, covers or parts of electric or electronic products, and the like, as it has a high melting point of 160 to 180° C., and is excellent in transparency. However, polylactic acid has a low crystallization rate, thus particularly in case where it is produced by injection molding in which orientation is not carried out, there are problems that the molded products are liable to have a low degree of crystallinity and deform at a temperature over glass transition temperature of about 60° C. In order to improve the degree of crystallinity, a process in which the mold temperature on injection molding is increased and the cooling time in the mold is elongated is attempted, but the process has a problem in productivity as a molding cycle is elongated. In order to produce polylactic acid resin compositions in a high productivity and use it for broad purpose, it is tried to increase crystallization rate and degree of crystallinity and improve forming processability and heat resistance.
As a method for increasing the crystallization rate of polylactic acid resin, for example a process in which a crystal nucleator is added is known. The crystal nucleator accelerates crystal growth by becoming a primary crystal nucleus of crystalline polymer and lower the crystal size, and improves the crystallization rate at the same time. The disclosed crystal nucleators for polylactic acid resins include inorganic particles composed of talc and/or boron nitride having a particle diameter of a specific level or less (see, Patent Document 1), amide compounds of a specific formula (see, Patent Document 2), sorbitol derivatives of specific formula (see, Patent Document 3), phosphoric acid ester metal salts and/or basic inorganic aluminum compounds (see, Patent Document 4), and the like. These methods can improve the crystallization rate and the degree of crystallinity. However, in recent years, for the accomplishment of higher forming processability and heat resistance, it is desired to develop further effective crystal nucleators. In addition, it is known that metal salts of phosphonic acid, phosphonous acid or the like are effective as a crystal nucleator for block copolymeric poly(ether ester) (see, Patent Document 5).    Patent Document 1: JP-A-8-3432 (1996) (Claims)    Patent Document 2: JP-A-10-87975 (1998) (Claims)    Patent Document 3: JP-A-10-158369 (1998) (Claims)    Patent Document 4: JP-A-2003-192883 (2003) (Claims)    Patent Document 5: JP-A-58-108249 (1983) (Claims)